A number of systems have been devised for constantly changing the color of a display or the like. My earlier patent, U.S. Pat. No. 3,694,054, issued on Sept. 26, 1972, illustrates a color-display system that maximizes the ratio of colored light to white light produced in a single cycle. This result is achieved by placing two birefringent sheets with different retardances between a pair of polarizing sheets whose light transmitting axes are orthogonal to one another, and rotating one of the birefringent sheets. As described in U.S. Pat. No. 3,694,054, that system is illuminated by a plurality of incandescent lamps, equally spaced around a control motor used for rotating one of the birefringent sheets.
That system, while functional for a variety of uses, has several limitations. Among other things, the multiple lamp arrangement produces hot spots, or areas where the light intensity is greater than average, at points in line with the lamps. In addition, should one of the lamps burn out, replacement is complicated by the inaccessible location of the lamp assemblies. Other disadvantages of a string of five, 24-volt bulbs in series are: (1) finding the one burned out bulb is difficult because one may have to try all five locations; (2) the string has an average lifetime which is shorter than the average lifetime of the individual bulbs (i.e., the lifetime for the string is equal to the lifetime of the worst bulb in the string rather than the average bulb); (3) a single, higher wattage bulb is intrinsically more durable than the miniature bulbs one fifth its size.